Aerosol methods for making chemical mechanical planarization (cmp) polishing pads

ABSTRACT

The present invention provides methods for making CMP polishing pads or layers therefore, the methods comprising introducing, separately, to a static mixer having a nozzle at its downstream end two solvent free and substantially water free components, a liquid polyol component having a temperature T 1  and a liquid isocyanate component having a temperature T 2 , each under a low gauge pressure of from 5 to 120 kPa (1 to 14 psi), the liquid polyol component comprising one or more polyol, an amine curative; and the liquid isocyanate component comprising one or more polyisocyanate or isocyanate-terminated urethane prepolymer; mixing the two components in the static mixer to form a reaction mixture, discharging a stream of the reaction mixture from the nozzle onto an open mold substrate having a urethane releasing surface, and curing to form a porous polyurethane reaction product.

The present invention relates to methods for producing porous polyurethane (PU) elastomer articles and chemical mechanical planarization (CMP) polishing pads comprising mixing in a static mixer and discharging therefrom at ambient pressure a solvent free and substantially water free two-component reaction mixture and onto to a mold, and curing to form the pad, wherein in the method no gas is injected into the reaction mixture and the reaction mixture is substantially free of blowing agents.

Known methods for producing porous CMP polishing pads include the addition of porous polymeric fillers, for example, into a molded polymeric matrix, mechanical frothing of a gas/polyurethane (PU) mixture that cures to trap gas bubbles; addition of blowing agents or using water to create pores from physically or chemically generated gas; and rapid decompression of polymers saturated with supercritical (SC) fluids (e.g. SC—CO₂). In any such methods, however, introduction of significant volumes of gas into a pad forming mixture gives rise to the need to condition the gas prior to its inclusion, and increases ventilation and effluent treatment requirements during and after processing. Known methods to generate or introduce gas to create pores into a pad forming mixture may not create a uniform pore distribution or uniformly fill molds to make CMP polishing pads. Further, introducing air or gas into or generating gas in such a reaction mixture for making CMP polishing pads can cause two phase flow from a spray device, which can lack homogeneity, alternating between liquid flow and gas flow at the spray tip or nozzle, resulting in an inhomogeneous material discharge and striation in the resulting product.

U.S. Pat. No. 8,314,029, to Hirose et al., discloses methods for making CMP polishing pads comprising preparing a cell-dispersed urethane forming composition by mechanical foaming and continuously discharging the composition from a single discharge port onto the central portion of a face material from which the polyurethane can be released while feeding the face material lengthwise, adjusting the thickness of the urethane forming composition on the face material, and curing the composition without applying an additional load to the composition. Mechanical foaming introduces unreactive gas into the reaction mixture.

The present inventors have sought to solve the problem of providing application or spray methods for making chemical mechanical polishing pads that have improved uniformity.

STATEMENT OF THE INVENTION

1. In accordance with the present invention, methods of making chemical mechanical planarization (CMP) polishing pads comprise introducing, separately, to a static mixer having a nozzle at its downstream end two solvent free and substantially water free components, a liquid polyol component having a temperature T1 and a liquid isocyanate component having a temperature T2, each under an absolute pressure of from 100 to 200 kPa or, preferably, from 100 to 150 kPa, to create flow through the mixer, the liquid polyol component comprising one or more polyol, an amine curative, preferably, an aromatic diamine, and further comprising a plurality of microelements, such as polymer microsphere beads; and the liquid isocyanate component comprising one or more polyisocyanate or isocyanate-terminated urethane prepolymer, preferably, an aromatic polyisocyanate or aromatic isocyanate-terminated urethane prepolymer; at least one component, preferably, the liquid polyol component comprising a sufficient amount of up to 2.0 wt. % or, preferably, from 0.1 to 1.0 wt. %, based on the total solids weight of the reaction mixture of a nonionic surfactant, preferably, an organopolysiloxane-co-polyether surfactant to facilitate stabilization of pores, mixing the two components in the static mixer to form a reaction mixture, discharging a stream of the reaction mixture from the nozzle onto a mold substrate having a urethane releasing surface, such as polytetrafluoroethylene, preferably, an open mold having a female topography that forms a desired groove pattern of a CMP polishing pad as the applied reaction mixture fills the mold and curing at from ambient temperature to 130° C. or, preferably, from ambient temperature to 100° C., to form a porous polyurethane reaction product having a density ranging from 0.6 gm/cc to 1 gm/cc or, preferably, from 0.75 gm/cc to 0.95 gm/cc.

2. In accordance with the methods of present invention for making CMP polishing pads as set forth in item 1, above, wherein the nozzle is equipped with an atomizing air inlet or air blast cap surrounding the outside of the nozzle, whereby a stream of air flows past the tip of the nozzle and then axially along the discharged stream of the reaction mixture.

3. In accordance with the methods of present invention for making CMP polishing pads as set forth in any one of items 1 or 2, above, wherein, the reaction mixture contains no added blowing agent, including no added chemical or physical blowing agents.

4. In accordance with the methods of present invention for making CMP polishing pads as set forth in any one of items 1, 2 or 3, above, wherein the reaction mixture has a gel time of 2 to 300 seconds or, preferably, from 5 to 60 seconds or, more preferably, from 5 to 45 seconds at the curing temperature.

5. In accordance with the methods of present invention for making CMP polishing pads as set forth in any of items 1, 2, 3 or 4, above, wherein upon introducing each of the liquid polyol component at temperature T1 and the liquid isocyanate component at temperature T2 to the static mixer, each has a viscosity of from 1 to 1000 cPs or, preferably, from 100 to 500 cPs, wherein each of T1 and T2 range from 10° C. to 80° C. or, preferably, range from 15 to 40° C. or, more preferably, are ambient temperature.

6. In accordance with the methods of present invention for making CMP polishing pads as set forth in item 5, above, further wherein, each of the liquid polyol component and the liquid isocyanate component is separately preheated, respectively, to temperature T1 and/or T2 before introducing it to the static mixer.

7. In accordance with the methods of present invention for making CMP polishing pads as set forth in any one of items 1, 2, 3, 4, 5 or 6, above, wherein the liquid polyol component further comprises one of a microelement, such as a polymer microsphere, or up to 3000 ppm or, preferably, up to 1500 ppm of water to enhance pad porosity.

8. In accordance with the methods of present invention for making CMP polishing pads as set forth in any one of items 1, 2, 3, 4, 5, 6 or 7, wherein the reaction mixture is solvent free and substantially water free.

9. In accordance with the methods of present invention for making CMP polishing pads as set forth in any previous items 1 to 8, above, wherein curing the reaction mixture comprises initially curing at from ambient temperature to 130° C. for a period of from 1 to 30 minutes, or, preferably, from 30 seconds to 5 minutes, removing the polyurethane reaction product from the mold, and then finally curing at a temperature from 60 to 130° C. for a period of 1 minutes to 16 hours, or preferably from 5 min to 15 minutes to form a porous article.

10. In accordance with the methods of the present invention as in item 10, above, wherein the forming of the polishing pad further comprises stacking a sub pad layer, such as a polymer impregnated non-woven, or porous or non-porous polymer sheet, onto bottom side of the porous article so that the molded surface of the porous article forms the top surface of a CMP polishing pad.

11. In accordance with the methods of the present invention as in any of items 1 to 10, above, wherein the discharging a stream of the reaction mixture onto a mold comprises overspraying the mold, followed by the curing the thus applied reaction mixture to form a polyurethane reaction product, removing the polyurethane reaction product from the mold and then punching or cutting the perimeter of the polyurethane reaction product to the desired diameter of the CMP polishing pad.

12. In accordance with the methods of the present invention as in any one of items 1 to 11, above, wherein the static mixer, including the nozzle at the downstream end thereof is held in place by a mechanical actuator that enables movement in a plane parallel to the surface of the open mold, such as, for example, a programmable electronic actuator having mechanical linkage enabling the programmed movement, preferably, a robot having a four axis arm capable of XY axial movement or a six axis arm capable of XYZ axial movement and rotational movement. For purposes of this specification, the formulations are expressed in wt. %, unless specifically noted otherwise.

Unless otherwise indicated, conditions of temperature and pressure are ambient temperature and standard pressure (101 kPa).

Unless otherwise indicated, any term containing parentheses refers, alternatively, to the whole term as if no parentheses were present and the term without them, and combinations of each alternative. Thus, the term “(poly)isocyanate” refers to isocyanate, polyisocyanate, or mixtures thereof.

All ranges are inclusive and combinable. For example, the term “a range of 50 to 3000 cPs, or 100 or more cPs” would include each of 50 to 100 cPs, 50 to 3000 cPs and 100 to 3000 cPs.

Unless otherwise indicated, as used herein, the term “average molecular weight” of a polymer refers to the result determined by gel permeation chromatography against the indicated or, if not indicated, known appropriate standards, such as poly(ethylene glycol)s for polyols.

As used herein, the term “gel time” means the result obtained by mixing a given reaction mixture at about 80° C., for example, in an VM-2500 vortex lab mixer (StateMix Ltd., Winnipeg, Canada) set at 1000 rpm for 30 s, setting a timer to zero and switching the timer on, pouring the mixture into an aluminum cup, placing the cup into a hot pot of a gel timer (Gardco Hot Pot™ gel timer, Paul N. Gardner Company, Inc., Pompano Beach, Fla.) set at 65° C., stirring the reaction mixture with a wire stirrer at 20 RPM and recording the gel time when the wire stirrer stops moving in the sample.

As used herein, the term “ASTM” refers to publications of ASTM International, West Conshohocken, Pa.

As used herein, the term “polyisocyanate” means any isocyanate group containing molecule containing two or more isocyanate groups.

As used herein, the term “polyurethanes” refers to polymerization products from difunctional or polyfunctional isocyanates, e.g. polyetherureas, polyisocyanurates, polyurethanes, polyureas, polyurethaneureas, copolymers thereof and mixtures thereof.

As used herein, the term “reaction mixture” includes any non-reactive additives, such as microelements and any additives to lower the hardness of a polyurethane reaction product in the CMP polishing pad according to ASTM D2240-15 (2015).

As used herein, the term “stoichiometry” of a reaction mixture refers to the ratio of molar equivalents of (free OH+free NH₂ groups) to free NCO groups in the reaction mixture.

As used herein, the term “SG” or “specific gravity” refers to the ratio of density of a polishing pad or layer made in accordance with the present invention to density of water at the same temperature.

As used herein, the term “solids” refers to any materials that remain in the polyurethane reaction product of the present invention; thus, solids include reactive and non-volatile additives that do not volatilize upon cure. Solids exclude water and volatile solvents.

As used herein, unless otherwise indicated, the term “substantially water free” means that a given composition has less than 2000 ppm, or, preferably, no added water and that the materials going into the composition have less than 2000 ppm, or, preferably, no added water. A reaction mixture that is “substantially water free” can comprise water that is present in the raw materials, in the range of from 50 to 2000 ppm or can comprise reaction water formed in a condensation reaction or vapor from ambient moisture where the reaction mixture is in use.

As used herein, the term “substantially free of blowing agents” means that a given composition contains no added chemical or physical blowing agent. Blowing agents do not include water. The air flow through the nozzle is not considered a part of a given composition.

As used herein, unless otherwise indicated, the term “viscosity” refers to the viscosity of a given material in neat form (100%) at a given temperature as measured using a rheometer, set at a steady shear of 1 rad/sec in a 50 mm parallel plate geometry with a 100 μm gap.

As used herein, the term “wt. %” stands for weight percent.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 is a depiction of a perspective view of an apparatus for use in the methods of the present invention.

The present invention enables a simple spray application method for making porous polyurethane CMP polishing pads from a two component reaction mixture, with no blowing agent and while avoiding gas injection by generating an aerosol after the liquid reacting mixture is discharged from the mixer exit. The only gas used in the methods of the present invention is ambient air. The pressures at which the fluid reaction mixtures are formed and applied to an open mold range from up to 200 kPa (at static mixer entry) to ambient pressure (at the static mixer downstream outlet). The methods of the present invention create porosity through entrapment of ambient air by the reaction mixture stream upon and after discharge into an open mold. Accordingly, when no microelements or polymer microspheres are present, the entrapped air forms pores, with average pore sizes ranging from 5 to 100 μm, or, preferably, from 10 to 40 μm. The low pressure of the methods of the present invention enable one to include microelements or fragile pore forming additives in the two component reaction mixture. Further, the simplicity and open mold nature of the methods of the present invention enables one to use very rapid curing reaction mixtures, such as those that have a gel time of 5 to 45 seconds, or a broader range of reaction mixtures that react more slowly, with a gel time of up to 300 seconds. Further, the methods of the present invention decouple the intensity or pressure of mixing from the degree of atomization of the reaction mixture generated during discharge, thereby allowing the formation of molded articles or CMP polishing pads having average pore sizes above 20 μm or even above 40 μm from a well mixed reaction mixture. Finally, the methods of the present invention and the low viscosity of the two-component reaction mixture together enable excellent mold filling and reproduction of the mold surface in the molded article or CMP polishing pad surface. The apparatus used in the methods of the present invention comprises a simple static mixer fed by two leads, one the liquid isocyanate component and the other the liquid polyol component, via a pump such as a peristaltic or positive displacement piston pump, and having a downstream spray nozzle equipped with an atomizing air cap. The static mixer operates from up to 200 kPa (at static mixer entry) to ambient pressure (at the static mixer outlet).

The spray nozzle of the present invention may be a simple conical nozzle equipped with a source of atomizing air surrounding the outside of the nozzle, for example, an air blast cap or atomizing air inlet. An air blast cap seats into the base of the nozzle and forms, together with the outside of the nozzle base an annular gap that allows ambient air to flow to the tip of the nozzle and then axially along the stream of discharged reaction mixture and onto the substrate. Suitable air blast caps and nozzles are available from Nordson EFD., Providence, R.I.

The air flow rate through the air blast cap or atomizing air inlet ranges from at a flow rate of from 20 to 180 L/min., or, preferably, from 30 to 150 L/min.

One suitable apparatus comprises two parts: Metering pumps feeding a controlled ratio of the liquid polyol component and the liquid isocyanate component from holding tanks to the static mixer, and a static mixer fitted with an air blast aerosolization tip that blends and sprays the reacting mixture onto the substrate.

The two leads into the static mixer in the apparatus of the present invention can comprise meter or delivery systems, such as a pair of pneumatically driven positive displacement piston pumps, each for dispensing the liquid polyol component or liquid isocyanate component through a series of fittings and tubing to the static mixer. The A/B ratio is controlled via a lever arm that mechanically varies the relative motion of the two piston pumps. An example of this equipment is commercially available as the Posiratio™ Mini PRM meter (Graco, Minneapolis, Minn.). Another example is two lab-grade peristaltic pumps to deliver, respectively, the liquid isocyanate component and liquid polyol component to the static mixer.

As shown in FIG. 1, static mixer (12) has two fluid inlet leads (16 and 18), one each for the liquid isocyanate component and the liquid polyol component, respectively. At its downstream end, static mixer (12) has a nozzle (20) equipped with an air blast cap (14) to assist in atomizing the spray from nozzle (20).

The reaction mixtures of the present invention comprise no solvent, and no added water except that up to 2000 ppm of water can be added to the liquid polyol component to facilitate pore formation.

The mold of the present invention is made of or is lined with a non-stick material, such as polytetrafluoroethylene. Preferably, the mold is machined to form a female topography so that the resulting molded polyurethane reaction product has a desired groove configuration.

Preferably, the substrate in the methods of the present invention is a mold wherein the produced CMP polishing pad will have groove pattern directly incorporated. For example, the mold may have a female topography that forms the groove pattern of the pad as the applied reaction mixture fills the mold.

The liquid isocyanate component of the present invention may comprise any of a diisocyanate, triisocyanate, isocyanurate isocyanate-terminated urethane prepolymer, or mixtures thereof. Preferably, the liquid isocyanate component comprises aromatic polyisocyanates, such as an aromatic diisocyanate chosen from methylene diphenyl diisocyanate (MDI); toluene diisocyanate (TDI); napthalene diisocyanate (NDI); paraphenylene diisocyanate (PPDI); o-toluidine diisocyanate (TODD; a modified diphenylmethane diisocyanate, such as a carbodiimide-modified diphenylmethane diisocyanate, an allophanate-modified diphenylmethane diisocyanate, a biuret-modified diphenylmethane diisocyanate: an aromatic isocyanurate, such as the isocyanurate of MDI; a linear isocyanate-terminated urethane prepolymer, for example, a linear isocyanate-terminated urethane prepolymer of MDI or an MDI dimer with one or more isocyanate extenders.

Suitable isocyanate extenders are ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol; 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, diethylene glycol; dipropylene glycol; tripropylene glycol, and mixtures thereof.

The liquid isocyanate component of the present invention can have a very high unreacted isocyanate (NCO) concentration of from 10 to 40 wt. %, or, preferably, from 15 to 35 wt. %, based on the total solids weight of the aromatic isocyanate component.

Suitable isocyanate-terminated urethane prepolymers are preferably isocyanate terminated urethane prepolymers having less than 0.1 wt. % free toluene diisocyanate (TDI) monomer content.

The liquid polyol component of the present invention can be anyone or more diols or polyether polyols having terminal hydroxyl groups, such as diols, polyols, polyol diols, copolymers thereof and mixtures thereof. Preferably, one or more polyol is chosen from polyether polyols (e.g., poly(oxytetramethylene)glycol, poly(oxypropylene)glycol and mixtures thereof); polycarbonate polyols; polyester polyols; polycaprolactone polyols; mixtures thereof; and, mixtures thereof with one or more low molecular weight polyols selected from the group consisting of ethylene glycol; 1,2-propylene glycol; 1,3-propylene glycol; 1,2-butanediol, 1,3-butanediol, 2-methyl-1,3-propanediol, 1,4-butanediol, neopentyl glycol; 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, diethylene glycol; dipropylene glycol; and, tripropylene glycol.

More preferably, the one or more polyol of the liquid polyol component of the present invention is chosen from polytetramethylene ether glycol (PTMEG); ester containing polyols (such as ethylene adipates, butylene adipates); polypropylene ether glycols (PPG); polycaprolactone polyols; copolymers thereof; and, mixtures thereof.

Suitable polyols can include a polyol having a number average molecular weight, M_(N), of 500 to 10,000. Preferably, the polyol used has a number average molecular weight, M_(N), of 500 to 6,000, or, more preferably 500 to 4,000; most preferably 1,000 to 2,000). Such a high molecular weight polyol preferably has an average of three to ten hydroxyl groups per molecule. More preferably, the high molecular weight polyol used has an average of four to eight, or, still more preferably five to seven, or, most preferably six hydroxyl groups per molecule. An example of a 6 hydroxyl group containing high molecular weight polyol is a polypropoxy-co-ethoxy sugar alcohol, such as sorbitol, having ethoxy hydroxyl groups.

The amine curative of the present invention is an amine or polyamine having one or more or, preferably, two or more amine groups, or, preferably, an aromatic polyamine, such as aromatic diamines and aromatic polyamines having three amine groups. More preferably, aromatic polyamine selected from the group consisting of dimethylthiotoluenediamine; trimethyleneglycol di-p-aminobenzoate; polytetramethyleneoxide di-p-aminobenzoate; polytetramethyleneoxide mono-p-aminobenzoate; polypropyleneoxide di-p-aminobenzoate; polypropyleneoxide mono-p-aminobenzoate; 1,2-bis(2-aminophenylthio)ethane, toluenediamines, such as diethyltoluenediamine, 5-tert-butyl-2,4-toluenediamine, 3-tert-butyl-2,6-toluenediamine, 5-tert-amyl-2,4-toluenediamine, 3-tert-amyl-2,6-toluenediamine, 5-tert-amyl-2,4-chlorotoluenediamine, and 3-tert-amyl-2,6-chlorotoluenediamine; methylene dianilines, such as 4,4′-methylene-bis-aniline; isophorone diamine; 1,2-diaminocyclohexane, bis(4-aminocyclohexyl)methane, 4,4′-diaminodiphenyl sulfone; m-phenylenediamine; xylene diamines; 1,3-bis(aminomethyl cyclohexane); and mixtures thereof, preferably, dimethylthiotoluenediamine.

Generally, the stoichiometric ratio of the sum of the total moles of amine (NH₂) groups and the total moles of hydroxyl (OH) groups in the reaction mixture to the total moles of unreacted isocyanate (NCO) groups in the reaction mixture ranges from 0.8:1.0 to 1.1:1.0, or, preferably, from 0.95 to 1.05.

The CMP polishing pad of the present invention may further comprise a plurality of microelements which, preferably, are uniformly dispersed throughout the polishing layer. Preferably, the microelements are selected from hollow core polymeric materials, such as polymeric microspheres, liquid filled hollow core polymeric materials, such as fluid filled polymeric microspheres, water soluble materials and insoluble phase materials (e.g., mineral oil). More preferably, the microelements are selected from hollow core polymeric materials. Preferably, the microelements have a weight average diameter of less than 150 μm, or, more preferably of less than 100 μm; most preferably of from 5 to 50 μm. Preferably, the plurality of microelements comprise polymeric microspheres with shell walls of either polyacrylonitrile or a polyacrylonitrile copolymer (e.g., Expancel™ beads from Akzo Nobel, Amsterdam, Netherlands). When used, the amount of microelements may range from the amount needed to generate in the CMP polishing pad or polishing layer from 0.1 to 50 vol. % porosity, or, preferably, 5 to 35 vol. % porosity. The term “porosity” refers to the volume concentration of the microelements divided by the volume of the resulting CMP polishing pad or layer.

The chemical mechanical polishing pads made by the methods of the present invention can comprise just a polishing layer of the polyurethane reaction product or the polishing layer stacked on a subpad or sub layer. The polishing pad or, in the case of stacked pads, the polishing layer of the polishing pad of the present invention is useful in both porous and non-porous or unfilled configurations.

Preferably, the polishing layer used in the chemical mechanical polishing pad of the present invention has an average thickness of from 500 to 3750 microns (20 to 150 mils), or, more preferably, from 750 to 3150 microns (30 to 125 mils), or, still more preferably, from 1000 to 3000 microns (40 to 120 mils), or, most preferably, from 1250 to 2500 microns (50 to 100 mils).

The chemical mechanical polishing pad of the present invention optionally further comprises at least one additional layer interfaced with the polishing layer. Preferably, the chemical mechanical polishing pad optionally further comprises a compressible sub pad or base layer adhered to the polishing layer. The compressible base layer preferably improves conformance of the polishing layer to the surface of the substrate being polished.

The polishing layer of the chemical mechanical polishing pad of the present invention has a polishing surface adapted for polishing the substrate. Preferably, the polishing surface has macrotexture selected from at least one of perforations and grooves. Perforations can extend from the polishing surface part way or all the way through the thickness of the polishing layer.

Preferably, grooves are arranged on the polishing surface such that upon rotation of the chemical mechanical polishing pad during polishing, at least one groove sweeps over the surface of the substrate being polished.

Preferably, the polishing layer of the chemical mechanical polishing pad of the present invention has a polishing surface adapted for polishing the substrate, wherein the polishing surface has a macrotexture comprising a groove pattern formed therein and chosen from curved grooves, linear grooves, perforations and combinations thereof. Preferably, the groove pattern comprises a plurality of grooves. More preferably, the groove pattern is selected from a groove design, such as one selected from the group consisting of concentric grooves (which may be circular or spiral), curved grooves, cross hatch grooves (e.g., arranged as an X-Y grid across the pad surface), other regular designs (e.g., hexagons, triangles), tire tread type patterns, irregular designs (e.g., fractal patterns), and combinations thereof. More preferably, the groove design is selected from the group consisting of random grooves, concentric grooves, spiral grooves, cross-hatched grooves, X-Y grid grooves, hexagonal grooves, triangular grooves, fractal grooves and combinations thereof. Most preferably, the polishing surface has a spiral groove pattern formed therein. The groove profile is preferably selected from rectangular with straight side walls or the groove cross section may be “V” shaped, “U” shaped, saw-tooth, and combinations thereof.

In accordance with the methods of making polishing pads in accordance with the present invention, chemical mechanical polishing pads can be molded with a macrotexture or groove pattern in their polishing surface to promote slurry flow and to remove polishing debris from the pad-wafer interface. Such grooves may be formed in the polishing surface of the polishing pad from the shape of the mold surface, i.e. where the mold has a female topographic version of the macrotexture.

The chemical mechanical polishing pad of the present invention can be used for polishing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate.

The CMP polishing pads of the present invention are efficacious for interlayer dielectric (ILD) and inorganic oxide polishing.

Preferably, the method of polishing a substrate of the present invention, comprises: providing a substrate selected from at least one of a magnetic substrate, an optical substrate and a semiconductor substrate (preferably a semiconductor substrate, such as a semiconductor wafer); providing a chemical mechanical polishing pad according to the present invention; creating dynamic contact between a polishing surface of the polishing layer and the substrate to polish a surface of the substrate; and, conditioning of the polishing surface with an abrasive conditioner.

Conditioning the polishing pad comprises bringing a conditioning disk into contact with the polishing surface either during intermittent breaks in the CMP process when polishing is paused (“ex situ”), or while the CMP process is underway (“in situ”). The conditioning disk has a rough conditioning surface typically comprised of imbedded diamond points that cut microscopic furrows into the pad surface, both abrading and plowing the pad material and renewing the polishing texture. Typically the conditioning disk is rotated in a position that is fixed with respect to the axis of rotation of the polishing pad, and sweeps out an annular conditioning region as the polishing pad is rotated.

EXAMPLES

The mixer/aerosol assembly is a Nordson Series 160AA disposable static mixer equipped with an Nordson Air Cap™ air blast assembly, Nordson EFD, Providence, R.I.). The air cap assembly, generally known as an air blast nozzle, is designed to fit over the end of the static mixer which has a nozzle with a given orifice size. The air blast nozzle is fed just downstream of the static mixer nozzle by a gas source (e.g. nitrogen or air) at a high velocity to aerosolize the PU mixture as it exits the end of the static mixer. The static mixer and air cap assembly are both disposable. The compositions used for spraying to make CMP polishing pads are shown below in Tables 1 and 2, below. All amounts in Tables 1 and 2 are weight parts as solids.

TABLE 1 Two Component Composition Example 1 Polyol Polytetrahydrofuran Terathane ™^(, 1) 851.136 T650 polyol Dimethylthio Ethacure ™^(, 2) 300 230.108 Toluenediamine (DMTDA) curative 1,4- Catalyst 6.000 Diazabicyclo[2.2.2]octane in dipropylene glycol Poly(siloxane-co-polyether) Surfactant (Niax ™^(, 3) 5.000 copolymer L-5345) NCO Methylene diphenyl Isonate ™^(, 4) 181 902.756 diisocyanate prepolymer, prepolymer 23 wt. % NCO Poly(siloxane-co-polyether) Surfactant 5.000 copolymer Polyol/NCO weight ratio 1.203 ¹ Invista, Wichita, KS; ² Chemtura Corp., Philadelphia, PA; ³ Momentive Performance Materials, Waterford, NY; ⁴ The Dow Chemical Co., Midland, MI).

TABLE 2 Two Component Composition Example Example 2A 2B Polyol Polytetrahydrofuran Terathane ™^(, 1) T650 8878.5 189.4 polyol Dimethylthio Ethacure ™^(, 2) 300 4734.3 101.0 Toluenediamine (DMTDA) curative Monoethylene glycol Chain extender 342.9 7.3 1,4- Catalyst 105 2.2 Diazabicyclo[2.2.2]octane in dipropylene glycol Expancel ™^(, 5) 461DE 20d70 Hollow polymer — 9.6 microsphere NCO Methylene diphenyl Isonate ™^(, 4) 181 15639 333.5 diisocyanate prepolymer, 23 prepolymer wt. % NCO Poly(siloxane-co-polyether) Surfactant (Niax ™^(, 3) 300 6.4 copolymer L-5345) Polyol/NCO weight 1.133 1.098 ratio ² Invista, Wichita, KS; ² Chemtura Corp., Philadelphia, PA; ³ Momentive Performance Materials Waterford, NY; ⁴ The Dow Chemical Co., Midland, MI); ⁵ Akzo Nobel, Arnhem, NL.

The composition was pumped into the static mixer at an absolute pressure of 110 kPa, mixed in the static mixer, and applied at ambient pressure to a 570 mm diameter polytetrafluoroethylene mold having a female topography which would yield a CMP polishing pad with a base thickness of 3 mm, and having a macrotexture in the form of a series of annular concentric elongated rectangular protrusions with cross-sectional dimensions of the protrusions 1.25 mm wide and 0.8 mm tall extending from the base pad. The spray fluid flow rate was controlled by pump speed entering the static mixer.

Example 1

The composition in Table 1, above, was sprayed at an air blast gas flow rate of 141.6 L/min., cured for 14 hours at 100° C. and demolded. Analysis of the cross-section images of the resulting article show that the average pore size is consistent from top to bottom of the sample, with few large bubbles and none larger than 100 μm. Average pore size for the cross-section was 27 μm. Preferred must have pore sizes at or below 40 um.

Examples 2A and 2B

The compositions in Table 2, above, were sprayed at an air blast gas flow rate ranging from 0-141.6 L/min. Table 3, below, lists density and measured mean pore diameter for final articles with the compositions at various atomizing air flow rates.

Test Methods:

The resulting molded articles were tested, as follows, and the results shown in Table 2, below:

Image Analysis:

Scanning electron micrographs (SEM) of the resulting moldings provided insight into their pore size averages. The images (not shown) used in the image analysis were a cross-section of the indicated molding from top to bottom (image 1=top, image 4=bottom).

Density was measured by an Archimedes method comparing the weight of a given molding vs. its weight when immersed in water.

Average pore size was measured by a manual image analysis of a selected number of pores (250-300 pores) to determine the pore diameter of each selected pore, which was then averaged.

TABLE 3 CMP Polishing Pad Pore Size And Density Blast Cap Air Flow Rate Density Mean Pore (L/min) (gm/cc) Diameter (um) Ex. 2B (With 0 0.96 Didn't measure microlements) 56.6 0.95 16.7 85 0.87 16.8 113.3 0.77 18.4 141.6 0.70 19.5 Ex. 2A 56.6 0.66 45.0 (Without 85 0.57 35.9 microelements) 113.3 0.56 35.5 141.6 0.57 34.6

As shown in Table 3, above, the gas flow rate though the air blast cap was critical to achieve the small average pore size and desired porosity. If the gas flow rate was too low, the generated fluid spray was too coarse and/or too low velocity to create the proper size of bubbles upon impacting the surface. Accordingly, in accordance with the present invention, the porosity and average pore size of a CMP polishing pad can be varied simply by changing the gas flow rate of the air blast cap in the apparatus. Thus, in Example 2A, very large pores can be formed even with thorough mixing in the static mixer; and the pore size of the applied and cured polyurethane reaction product is independent of the amount or quality of mixing in the static mixer.

Regarding average pore size, Table 2, above, shows that as the flow rate drops from 141.6 normal liters per minute (L/min) to 56.6 L/min, the average size of the pores increases dramatically, and the number of pores drops. Based on these data, an air flow rate of 85 L/min is preferred, with 141.6 L/min most preferred to achieve desired CMP polishing pad average pore size. The density of the moldings correspond inversely to gas flow rate, from ˜0.8 gm/cc at the highest gas flow rate, to ˜0.95 gm/cc at the lowest gas flow rate. The compositions with microelements provide a density and an average pore size in the preferred range for a CMP polishing pad.

As shown in Table 3, above, the methods of the present invention enable one to spray reaction mixtures to generate pores either through entrapment of ambient air, as demonstrated above, or via the addition of polymeric microspheres. In the Example 2 articles sprayed with microspheres, the microspheres make up most of the observed pores. This evidences excellent control over and predictability of porosity. The uniformity of average pore sizes of in the top line indicate that the microspheres remained intact throughout the process. The articles of Example 1, without polymeric microspheres have a similar density, and pores only from entrapped air, evidencing the flexibility of the methods of the present invention. 

We claim:
 1. A method of forming a chemical mechanical planarization (CMP) polishing pad comprising introducing, separately, to a static mixer having a nozzle at its downstream end two solvent free and substantially water free components, a liquid polyol component having a temperature T1 and a liquid isocyanate component having a temperature T2, each under an absolute pressure of from 100 to 200 kPa, the liquid polyol component comprising one or more polyol, an amine curative; and the liquid isocyanate component comprising one or more polyisocyanate or isocyanate-terminated urethane prepolymer; at least one component, comprising a sufficient amount of up to 2.0 wt. %, based on the total solids weight of the reaction mixture of a nonionic surfactant to facilitate stabilization of pores, mixing the two components in the static mixer to form a reaction mixture, discharging a stream of the reaction mixture from the nozzle at ambient pressure onto a mold substrate having a urethane releasing surface, and curing at from ambient temperature to 130° C. to form a porous polyurethane reaction product having a density ranging from 0.6 gm/cc to 1 gm/cc.
 2. The method as claimed in claim 1, wherein the nozzle is equipped with an atomizing air inlet or air blast cap surrounding the outside of the nozzle whereby a stream of air flows past the tip of the nozzle and then axially along the discharged stream of the reaction mixture.
 3. The method as claimed in claim 1, wherein, the reaction mixture contains no added chemical or physical blowing agents.
 4. The method as claimed in claim 1, wherein the reaction mixture has a gel time of 2 to 300 seconds at the curing temperature.
 5. The method as claimed in claim 1, wherein upon introducing each of the liquid polyol component at temperature T1 and the liquid isocyanate component at temperature T2 to the static mixer, each has a viscosity of from 1 to 1000 cPs.
 6. The method as claimed in claim 1, wherein in the liquid polyol component, the amine curative is an aromatic diamine.
 7. The method as claimed in claim 1, wherein the liquid polyol component further comprises a plurality of microelements.
 8. The method as claimed in claim 1, wherein in the liquid isocyanate component, the isocyanate comprises an aromatic polyisocyanate or aromatic isocyanate-terminated urethane prepolymer.
 9. The method as claimed in claim 1, wherein the mold substrate comprises an open mold having a female topography that forms a desired groove pattern of a CMP polishing pad as the applied reaction mixture fills the mold.
 10. The method as claimed in claim 1, wherein curing the reaction mixture comprises initially curing at from ambient temperature to 130° C. for a period of from 1 to 30 minutes, removing the polyurethane reaction product from the mold, and then finally curing at a temperature from 60 to 130° C. for a period of 1 minutes to 16 hours to form a porous article. 